The biodegradability of polyaspartic acids makes them particularly valuable from the point of view of environmental acceptability and waste disposal. After polyaspartic acid has been utilized, it biodegrades to environmentally acceptable end products.
Anhydropolyaspartic acids (i.e. polysuccinimides) are the anhydrous forms of polyaspartic acids.
Thermal condensation of aspartic acid to produce polyaspartic acid is taught by Etsuo Kokufuta, et al., "Temperature Effect on the Molecular Weight and the Optical Purity of Anhydropolyaspartic Acid Prepared by Thermal Polycondensation", Bulletin of the Chemical Society Of Japan, Vol. 51 (5), 1555-1556 (1978). Kokofuto teaches that the molecular weight of the polyaspartic acid produced by this method increases with increased reaction temperature. Moreover, the maximum percent conversion of the aspartic acid to anhydropolyaspartic acid suggested is no more than 68% using oil bath temperatures of between 325.degree. F and 425.degree. F.
A more recent work by Brenda J. Little et al, "Corrosion Inhibition By Thermal Polyaspartate" Surface Reactive Peptides and Polymers, pp 263-279, American Chemistry Society Symposium Series 444(1990), cited Kokofuto. Oil bath temperatures of 374 .degree. F were used to produce anhydropolyaspartic acid from powdered aspartic acid over a period of 24 to 96 hours. The results were no better than Kokofuto's.
Calcium phosphate and calcium carbonate inhibitors are used in a number of applications to prevent precipitation and scale formation. Included among these are cooling water treatment, boiler water treatment, desalination, reverse osmosis, flash evaporators, oil field recovery operations, and for plaque and tartar control.
It is known that polyaspartic acids have utility as calcium carbonate inhibitors. U.S. Pat. No. 4,534,881, at col 14, Table 4, teaches a calcium carbonate activity test lag phase of 120 minutes for a 0.05 .mu.g/1 polyaspartate concentration at 20.degree. C.
It is known that polyaspartic acids inhibit calcium phosphate crystallization. "Inhibition of Calcium Carbonate and Phosphate Crystallization by Peptides Enriched in Aspartic Acid and Phosphoserine," by Sikes et al, ACS Symposium Series 444 (1991).